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| United States Patent |
5,070,143
|
|
Pucci
, et al.
|
December 3, 1991
|
Adhesive blend of polyolefins and grafted block copolymer of polystyrene
Abstract
Composition comprising a mixture of from about 30% to about 99.9% of a
polyolefin base resin; from about 0.1% to about 50% of a graft polymerized
block copolymer having polystyrene end blocks and an aliphatic middle
block; from 0 to about 40% by weight of an elastomer different from the
above components; and from 0 to about 30% by weight of a nonelastomeric
second polyolefin made from different monomers from those of the
polyolefin base resin. The composition can be used as an adhesive film or
tie layer, optinally by coextrusion between layers to be joined. Coatings
and coated substrates are also disclosed.
| Inventors:
|
Pucci; Mark S. (Elk Grove Village, IL);
Shida; Mitsu (Barrington, IL);
Machonis, Jr.; John (Schaumburg, IL);
Jachec; Kevin (Highwood, IL)
|
| Assignee:
|
Morton International, Inc. (Chicago, IL)
|
| Appl. No.:
|
321485 |
| Filed:
|
March 9, 1989 |
| Current U.S. Class: |
525/74; 524/505; 525/78; 525/941 |
| Intern'l Class: |
C08L 023/06; C08L 023/08; C08L 023/12; C08L 053/02 |
| Field of Search: |
525/74,78
|
References Cited
U.S. Patent Documents
| 3483276 | Dec., 1969 | Mahlman.
| |
| 3562356 | Feb., 1971 | Nyberg et al. | 525/93.
|
| 3630980 | Dec., 1971 | Russell | 525/93.
|
| 3697465 | Oct., 1972 | Joyner et al.
| |
| 3746676 | Jul., 1973 | Joyner et al.
| |
| 3886227 | May., 1975 | Van Brederode et al.
| |
| 4058647 | Nov., 1977 | Inone et al.
| |
| 4087587 | May., 1978 | Shida et al.
| |
| 4087588 | May., 1978 | Shida et al.
| |
| 4198327 | Apr., 1980 | Matsumoto et al.
| |
| 4308353 | Dec., 1981 | Saito et al. | 525/74.
|
| 4423117 | Dec., 1983 | Maconis, Jr. et al.
| |
| 4477532 | Oct., 1984 | Schmukler et al.
| |
| 4570286 | Feb., 1986 | Ross.
| |
| 4578429 | Mar., 1986 | Gergen et al.
| |
| 4628072 | Dec., 1986 | Shiraki et al. | 525/98.
|
| 4835218 | May., 1989 | Yoshimura et al. | 525/98.
|
| 4868245 | Sep., 1989 | Pattick et al. | 525/98.
|
| 4904728 | Feb., 1990 | George | 525/98.
|
| 4906687 | Mar., 1990 | Modic | 525/98.
|
| Foreign Patent Documents |
| 60-101130 | Jun., 1985 | JP.
| |
| 1119629 | Jul., 1968 | GB.
| |
| 1335791 | Oct., 1973 | GB.
| |
Other References
"Plastics Technology", Oct. 1987.
"Modern Plastics International", Sep., 1987.
"Technical Bulletin ShellChemical Compnay", Kraton FG 1901X Rubber brochure
#SC:592-87.
|
Primary Examiner: Seccuro; Carman J.
Attorney, Agent or Firm: Nacker; Wayne E., White; Gerald K.
Claims
We claim:
1. An adhesive composition consisting of a mixture of:
A. from about 30% to about 99.9% by weight of a polyolefin base resin
selected from the group consisting of polypropylene; polyethylene; and
compolymers of ethylene with vinyl acetate, vinyl alcohol, methyl
acrylate, methylmethacrylate, ethyl acrylate, and ethyl methacrylate;
B. from about 0.1% to about 50% by weight of a graft polymerized block
copolymer having polystyrene end blocks and at least one polymer of an
olefin, diolefin, or mixture thereof or a hydrogenated polymer thereof as
a middle block, graft polymerized by treatment with at least one monomer
selected from carboxylic acids, their anhydrides, and mixtures thereof;
C. from 0 to about 30% by weight of a nonelastomeric second polyolefin made
from different monomers from those of said polyolefin base resin; and
optional fillers, adhesion promoters and antioxidants.
2. The composition of claim 1, wherein said base resin consists essentially
of polypropylene.
3. The composition of claim 1, containing from about 70% to about 98% by
weight of said base resin.
4. The composition of claim 1, wherein the middle block of said graft
polymerized block copolymer consists essentially of hydrogenated
polybutadiene.
5. The composition of claim 1, wherein said graft-polymerized block
copolymer is an ABA block copolymer having about 28% by weight polystyrene
end blocks and 70% by weight of a middle block consisting essentially of
hydrogenated polybutadiene, grafted with about 2% by weight maleic
anhydride.
6. The composition of claim 1, wherein said monomer is maleic anhydride.
7. The composition of claim 1, containing from about 2% to about 30% by
weight of said graft-polymerized block copolymer.
8. The composition of claim 1, containing from about 70% to about 98% by
weight said base resin.
9. The composition of claim 1, wherein said base resin consists essentially
of polypropylene and said nonelastomeric second polyolefin consists
essentially of polyethylene.
10. The composition of claim 1, containing from about 10% to about 20% by
weight of said nonelastomeric second polyolefin.
11. The composition of claim 1, wherein said base resin consists
essentially of a copolymer of ethylene and vinyl acetate.
12. The composition of claim 1, wherein said base resin consists
essentially of a copolymer of ethylene and methyl acrylate.
13. The composition of claim 1, wherein said base resin consists
essentially of a copolymer of ethylene and ethyl acrylate.
14. The composition of claim 10, wherein said base resin consists
essentially of polypropylene and said nonelastomeric second polyolefin
consists essentially of polyethylene.
Description
TECHNICAL FIELD
The present invention relates to a polyolefin-based composition suitable
for adhering to polar or nonpolar substrates, or for joining polyolefins
to polar or nonpolar polymers. One particular application of the
composition is as an extrudible adhesive tie resin to join adjacent,
coextruded layers.
BACKGROUND
Composite packaging structures including one or more fluid-impermeable or
heat-sealable layers of a polyolefin such as polyethylene or polypropylene
and one or more oxygen impermeable or otherwise functioning layers of a
polar polymer, such as nylon and others, are well known. One continuing
problem is how to join a nonpolar polyolefin and a polar polymer to
achieve the highest possible adhesion. Polar and nonpolar materials do not
adhere directly, and it is difficult to formulate an adhesive which
adheres to both polar and nonpolar materials with optimal adhesive
strength.
An early, partial solution to this problem, which is still employed widely,
is an adhesive consisting essentially of a polyolefin blended with a graft
copolymer of the same polyolefin. The graft monomer is a carboxylic acid
or anhydride. The most widely used graft monomers are maleic anhydride and
acrylic acid, particularly the former. The first commercially prominent
version of this graft copolymer was the HERCOPRIME series of maleic
anhydride-modified polypropylenes sold by Hercules Inc. (See U.S. Pat.
Nos. 3,483,276 and 4,570,286). Now there are many commercial sources of
this and other graft polymerized polyolefins.
Representative patents describing blends of a polyolefin and its graft
copolymer are as follows: U.S. Pat. Nos. 3,697,465 (column 3, lines 64-67)
and 3,746,676 (column 3, lines 32-37), each issued to Joyner, et al.,
specifically teach that the maleated copolymer should be based on the same
resin as the polyolefin base material. U.S. Pat. Nos. 4,087,587 and
4,423,117 describe a polyethylene base material combined with a graft
copolymer of polyethylene. U.S. Pat. No. 4,477,532 (column 1, lines 12-30)
and British Patent No. 1,335,791 teach a polypropylene base material
combined with grafted polypropylene.
In the next generation of polyolefin adhesives, an elastomer was added to
further improve adhesion to polar substrates. Exemplary patents are U.S.
Pat. Nos. 4,058,647; 4,198,327; 3,886,227; 4,423,117; and the two Joyner
patents previously cited.
A related problem in the art has been how to adhere polyolefin-based
coatings to metals, which are also polar substrates. The art has improved
the adhesion of polyolefin-based coatings to metals by adding graft
copolymers and elastomers to the polyolefin.
A common theme in all this development has been the combination of a
graft-polymerized polyolefin with an unmodified polyolefin base material.
Identical or similar resins have been used for the base material and
grafted resin to ensure that the base material and graft copolymer will be
compatible and homogeneous when blended.
The use of a graft-copolymerized elastomer by itself or in combination with
the unmodified elastomer as an adhesive is described in U.S. Pat. No.
4,578,429 (three-block copolymer having polystrene end blocks and an
ethylene/butadiene copolymer middle block, grafted with maleic anhydride)
and British Patent No. 1,119,629.
SUMMARY OF THE INVENTION
The inventors have discovered that the adhesion of a blend of a polyolefin
base material and a graft copolymer to polar and nonpolar substrates can
be improved by selecting a grafted block copolymer having aromatic end
blocks (preferably polystyrene) and an aliphatic middle block as the graft
copolymer. Surprisingly, this combination provides better adhesion to a
variety of polar substrates than the known combination of a polyolefin
base material and its graft copolymer, even if the prior art graft
copolymer being compared is elastomeric.
The composition described in the preceding paragraph can be further
improved by adding a conventional elastomer to the formulation, and still
further improved by adding to the composition a nonelastomeric second
polyolefin made from a different monomer than the base polyolefin is made
from.
Improved methods of adhering substrates together, improved laminated
structures in which polar and nonpolar layers are joined, and a polar or
nonpolar substrate coated with the present compositions are also part of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The compositions described herein are mixtures of from about 30% to about
99.9% of a polyolefin base resin, from about 0.1% to about 50% of a
grafted block copolymer having aromatic (preferably polystyrene) end
blocks and an aliphatic middle block, from 0% to about 40% by weight of
conventional elastomer, and from 0% to about 30% by weight of a
nonelastomeric polyolefin different from the base polyolefin. Preferred
proportions of the principal ingredients are from about 70% to about 98%
by weight of the base resin and from about 2% to about 30% by weight of
the graft polymerized block copolymer. For three-component blends the
relevant proportions preferred herein are from about 50% to about 93% by
weight of the base resin, from about 2% to about 20% by weight of the
graft copolymer, and from about 5% to about 30% by weight of the
elastomer. For four-component blends the preferred proportions are from
about 30% to about 83% by weight of the base resin, from about 2% to about
20% by weight by weight of the graft polymerized block copolymer, from
about 5% to about 30% of the conventional elastomer, and from about 10% to
about 20% by weight of the nonelastomeric second resin. Each of these
materials is described more thoroughly below. Further exemplification of
these materials can be found by reference to any of the previously
identified patents, which are hereby incorporated herein by reference.
The polyolefin base resins preferred herein can be any of the well known
homopolymers or copolymers of alpha-olefins, particularly any of those
described in the previously incorporated patents. Preferred examples are
polypropylene or polyethylene in any of their known embodiments, some of
which are copolymers with minor amounts of other olefins or polar
materials such as vinyl acetate, vinyl alcohol, methyl acrylate, methyl
methacrylate, ethyl acrylate, ethyl methacrylate, or others. One example
of a copolymer useful herein is EVA - the copolymer of a minor amount of
vinyl acetate and a major amount of ethylene. Two more examples are
copolymers of ethylene and methyl acrylate and copolymers of ethylene and
ethyl acrylate.
The grafted block copolymers preferred herein are the reaction products of
(1) a grafting monomer; and (2) a block copolymer of polystyrene with an
aliphatic middle block. the grafting monomer can be any of those in the
previously incorporated patents, and preferably is maleic anhydride. The
block copolymer is preferably an "ABA" copolymer in which the end blocks
("A" blocks) are polystyrene and the "B" or middle block is an aliphatic
polymer. Examples of middle blocks useful herein are homopolymers or
copolymers of butadiene, hydrogenated butadiene, isoprene, and
hydrogenated isoprene. Block copolymers contemplated in the present
invention contain from about 20% by weight to about 40% by weight
polystyrene end blocks and from about 60% to about 80% by weight of the
middle block.
The reaction product of (1) and (2) is prepared by blending the reactants
in an extruder or other mixer or in solvent dispersion, along with a
reaction initiator, such as an organic peroxide. Typically, (2) is by far
the dominant ingredient, comprising 97% or more of the product by weight.
A commercial example of (2) is the KRATON series of thermoplastic rubbers
sold by Shell Chemical Co., Houston, Tex. A commercial example of the
graft copolymer is KRATON FG 1901 X maleic anhydride modified
thermoplastic rubber, also sold by Shell Chemical Co. The latter material
contains 28% by weight polystyrene as the end blocks, 70% of hydrogenated
butadiene as the middle block, and 2% bound maleic anhydride. Its Shore A
hardness is 75, and its specific gravity is 0.91 g/cc.
The conventional elastomers useful herein are any of those specified in the
patents previously incorporated herein by reference. One preferred
elastomer is "EPR", a copolymer of ethylene and propylene which is
elastomeric and thermoplastic. A useful commercial material of this kind
is POLYSAR EPM 306, sold by Polysar Inc., Akron, Ohio. Thermoplastic
elastomers are preferred, as are elastomers which are compatible with the
other ingredients of the composition.
Nonelastomeric second polyolefins contemplated for use herein are any of
the materials described previously as suitable base resins, but have a
different predominant monomer than the selected base resin and are present
as a substantially smaller proportion of the composition than the base
resin. One example of a nonelastomeric second polyolefin contemplated
herein is high density polyethylene, used with a polypropylene base resin.
A specifically contemplated nonelastomeric second polyolefin is CHEVRON
9634 polyethylene, available from Chevron Chemical Co., San Francisco,
Calif.
Other ingredients can be added to the present compositions in amounts which
do not destroy their contemplated utility. Three examples are fillers,
adhesion promoters, and antioxidants.
The ingredients of the present compositions can be blended in many ways,
preferably by tumbling particulate ingredients together thoroughly and
passing the composite through an extruder which mixes the ingredients to
form a homogeneous composition having consistent proportions. The
composition can be provided as pellets or noodles suitable for being
processed in a coextrusion line, or directly as an extruded product formed
from the ingredients in a one-step process.
The present compositions can be provided or used as primers or tie layers,
as formed films or sheets capable of being laminated between formed
substrate films or sheets or receiving a freshly extruded film or sheet of
either or both substrates, as dispersions in a solvent, as powder coatings
or fluid-applied (molten or solvent-based) coatings on aluminum, other
metals and other polar and nonpolar substrates, or otherwise. One
particular contemplated way of forming a composite structure of the
present composition and a substrate is to coextrude the respective
materials.
Laminates according to the present invention can comprise two facing layers
joined by an intermediate tie layer of the present composition,
functioning as an adhesive. Additional layers are also contemplated. For
example if polar layers are "A", tie layers are "B", and nonpolar layers
are "C", laminates of the present invention can comprise an "ABA", "CBC",
or "ABC" three-layered structure. Multilayer laminates containing the
"ABC" core structure can include "ABCBA", "CBABC", or "ABCCBA" structures,
or even "ABCB" laminates in which an outer layer is made of a composition
according to the present invention.
The compositions of the present invention adhere better than previous
compositions to a wide variety of nonpolar substrates such as any of the
polyolefins previously specified, polydiolefins, polystyrene, copolymers
and mixtures thereof, and copolymers thereof with minor amounts of
polyvinyl acetate or polyvinyl alcohol, and to a wide variety of polar
substrates such as polyamides, polyethers, polyesters, polyvinyl acetate,
polyvinyl alcohol, polymethyl acrylate, polyethyl acrylate, polyethyl
methacrylate, ethylene vinyl alcohol copolymers (EVOH), polycarbonate,
mixtures and copolymers of any of the foregoing, copolymers thereof with
minor amounts of polyolefins or polydiolefins, aluminum or other metals in
foil or rigid form, wood, paper, etc. Of particular value is the high
total adhesion between a polar substrate and a nonpolar substrate provided
by a tie layer of the present composition, functioning as an adhesive.
This property is measured by laminating a polar substrate, a nonpolar
substrate, and an intermediate tie layer and measuring the ability of the
composite to withstand delamination. Delamination is likely to occur at
the weaker of the two interfaces between the three layers. An adhesive
which adheres tightly to each substrate has a higher total adhesion than
an adhesive which adheres tightly to one substrate and less tightly to
another. Two nonpolar substrates or two polar substrates can also be
joined using the present composition, functioning as an adhesive.
EXAMPLES 1-2
Adhesive compositions substantially according to the prior art (Example 1)
and according to the present invention (Example 2) were formed by
extruding and pelleting the formulas stated in Table 1 in a single-screw
extruder. Tie layers of each composition were coextruded with alternating
layers of polypropylene and an EVOH copolymer (SOARNOL DC, sold by Nippon
Gohsei, Osaka, Japan) on a laboratory cast film line at a melt temperature
of 420.degree. F. (216.degree. C.) to provide five-layer films consisting
of the following layers in order: polypropylene/tie layer/EVOH/tie
layer/poly- propylene. One film was 178 microns (7 mils) thick and the
other was 254 microns (10 mils) thick for each tie layer formulation. Each
film was then tested for T-peel adhesion on an Instron at a crosshead
speed of 10 inches per minute (4.2 mm per second). The peel was started
between one of the tie layers and the EVOH layer. The adhesion results
were as stated in Table 2.
Examples 1 and 2 illustrate the surprising result that combining the graft
copolymer of one resin with a different base resin (polypropylene),
instead of combining the graft copolymer of polypropylene with more
polypropylene, actually increased the adhesion of the tie layer. According
to prior knowledge, a decrease in adhesion would be expected.
EXAMPLES 3-8
Coextruded films including as tie layers the three-component blends having
the formulations shown in Tables 3, 5, and 7 were prepared as described in
Examples 1 and 2. The adhesion results are shown in Tables 4, 6, and 8.
Examples 3 and 4, Tables 3 and 4, illustrate that the adhesion of a
three-component blend of polypropylene, and elastomer, and grafted
polypropylene was improved substantially by substituting the grafted
polystyrene block copolymer of Example 4 for the grafted polypropylene of
Example 3.
Examples 5 and 6 employ adhesive compositions within the scope of the
present invention. These examples illustrate that in the preferred
embodiment, the replacement of some of the polypropylene base material
with polyethylene surprisingly and substantially improved adhesion.
Examples 7 and 8, Tables 7 and 8, illustrate that the invention works with
a polyethylene base resin, and that adhesion can be substantially improved
if a conventional grafted EPR elastomer is replaced with a grafted
polystyrene block copolymer according to the present invention.
TABLE 1
______________________________________
Comparative
Example 1 Example 2
Ingredient % by weight
% by weight
______________________________________
Polypropylene.sup.1
75% 75%
grafted polypropylene.sup.2
25% --
grafted polystyrene
-- 25%
block copolymer.sup.3
Total 100% 100%
______________________________________
.sup.1 ESCORENE 4092 sold by Exxon Chemicals, Houston, Texas.
.sup.2 HERCOPRIME A, sold by Himont USA, Wilmington, Delaware.
.sup.3 KRATON FG 1901X, sold by Shell Chemical Company, Houston, Texas.
TABLE 2
______________________________________
Example Film Thickness
Adhesion to EVOH
______________________________________
1 (comparative)
7 mil (0.18 mm)
0.6 lb/in (107 g/cm)
2 7 mil (0.18 mm)
1.6 lb/in (286 g/cm)
1 (comparative)
10 mil (0.25 mm)
1.5 lb/in (268 g/cm)
2 10 mil (0.25 mm)
3.6 lb/in (642 g/cm)
______________________________________
TABLE 3
______________________________________
Comparative
Example 3 Example 4
Ingredient % by weight
% by weight
______________________________________
polypropylene.sup.1
65% 65%
EPR elastomer.sup.2
20% 20%
grafted polypropylene.sup.3
15% --
grafted polystyrene
-- 15%
block copolymer.sup.4
Total 100% 100%
______________________________________
.sup.1 ESCORENE 4092, sold by Exxon Chemicals, Houston, Texas.
.sup.2 POLYSAR EPM 306, sold by Polysar Incorporated, Akron, Ohio.
.sup.3 HERCOPRIME A, sold by Himont USA, Houston, Texas.
.sup.4 KRATON FG 1901 X, sold by Shell Chemical Co., Houston, Texas.
TABLE 4
______________________________________
Example Film Thickness
Adhesion to EVOH
______________________________________
3 (comparative)
7 mil (0.18 mm)
0.3 lb/in (53 g/cm)
4 7 mil (0.18 mm)
0.8 lb/in (143 g/cm)
3 (comparative)
10 mil (0.25 mm)
1.2 lb/in (214 g/cm)
4 10 mil (0.25 mm)
3.3 lb/in (589 g/cm)
______________________________________
TABLE 5
______________________________________
Example 5 Example 6
Ingredient % by weight
% by weight
______________________________________
polypropylene.sup.1
65% 50%
EPR elastomer.sup.1
20% 20%
grafted block copolymer.sup.1
15% 15%
high-density polyethylene.sup.2
-- 15%
Total 100% 100%
______________________________________
.sup.1 Same as in Table 3.
.sup.2 CHEVRON 9634, sold by Chevron Chemical Co., San Francisco,
California
TABLE 6
______________________________________
Example Film Thickness Adhesion to EVOH
______________________________________
5 8 mil (0.20 mm)
1.5 lb/in (268 g/cm)
6 8 mil (0.20 mm)
2.9 lb/in (517 g/cm)
5 10 mil (0.25 mm)
3.3 lb/in (589 g/cm)
6 10 mil (0.25 mm)
5.5 lb/in (981 g/cm)
______________________________________
TABLE 7
______________________________________
Comparative
Example 7 Example 8
Ingredient % by weight % by weight
______________________________________
polyethylene copolymer (EVA).sup.1
94% 94%
grafted EPR elastomer.sup.2
6% --
grafted polystyrene
-- 6%
block copolymer.sup.3
Total 100% 100%
______________________________________
.sup.1 ESCORENE 324.55, sold by Exxon Chemicals, Houston, Texas.
.sup.2 XX1601, sold by Exxon Chemicals, Houston, Texas.
.sup.3 KRATON FG 1901X, sold by Shell Chemical Company, Houston, Texas.
TABLE 8
______________________________________
Example Film Thickness
Adhesion to EVOH
______________________________________
1 (comparative)
3 mil (0.08 mm)
0.4 lb/in (71 g/cm)
2 3 mil (0.08 mm)
1.4 lb/in (250 g/cm)
1 (comparative)
5 mil (0.13 mm)
1.3 lb/in (232 g/cm)
2 5 mil (0.13 mm)
3.2 lb/in (572 g/cm)
______________________________________
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